"Raj and Aamir are not friends."
Translation:राज और आमिर दोस्त नहीं हैं।
ं (ँ when no vowel diacritic interfering like ै, and not denoting an न-first conjunct) nasalises the vowel. The degree to which speakers distinguish it may vary of course, not least because - as a non-native speaker/learner - I find it pretty difficult to nasalise vowels (especially without way over exaggerating it!).
In Hindi, you 'make friendship' with someone - राज ने आमिर से दोस्ती कर ली or राज ने आमिर के साथ दोस्ती कर ली (Raj became friends with Aamir).
However, you are someone's friend (not 'friends with someone') - राज आमिर का दोस्त है (Raj is Aamir's friend).
So, के साथ -'with' doesn't fit in this sentence.